Broadband dual-polarized antenna



Dec. 12, 1967 H. BRUECKMANN BROADBAND DUAL-POLARIZED ANTENNA 2Sheets-Sheet 1 Filed Jan.

FIG. 3

INVENTOR, HEL MUT BRUECKMANN.

w: ,m& M ATTORNEYS Dec. 12, 1967 H. BRUECKMANN BROADBAND DUAL-POLARIZEDANTENNA 2 Sheets-Sheet 2 Filed Jan. 6, 1965 FIG. 4

INVENTOR.

HELMUT BRUECKMANN BY W1- I W M C ATTORNEYS United States Patent3,358,287 BROADBAND DUAL-POLARIZED ANTENNA Helmpt Brueckmann, LittleSilver, N.J., assignor to the United States of America as represented bythe Secretary of the Army Filed Jan. 6, 1965, Ser. No. 423,881 8 Claims.(Cl. 343-786) ABSTRACT OF THE DISlZ'LOSURE A dual-polarized turnstileantenna having two sets of orthogonally spaced dipoles. A pair of inputsare coupled to the antenna via a transformer arrangement such that twoadjacent antenna elements are fed in phase with each other and fedagainst the other two elements as viewed from one of the inputs. Asviewed from the other input a difierent set of two adjacent antennaelements are fed in phase with each other and fed against the other twoelements.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment of anyroyalty thereon.

The present invention relates to improvements in antennas and the likeand more particularly to an improved feed system for broadbandingdual-polarized antennas.

It is well known that any type and orientation of polarization ofelectromagnetic waves can be obtained by arranging two dipolesorthogonally about a common center and exciting them in the proper phaseand ampli tude relationship. Such an arrangement is commonly referred toas a turnstile antenna and falls in the general classification ofdual-polarized antennas, i.e., an antenna having two planes ofpolarization which are perpendicular to each other. It is now standardpractice to thicken the antenna elements or conductors as one means forbroadbanding turnstile antennas. This method, however, has thedisadvantage of increasing wind drag, ice load, etc. compared tonarrowband antennas having relatively thin antenna elements. As aresult, construction costs including the cost of the support arerelatively high. Another standard method of broadbanding such elementsis to increase the number of antenna elements. However, it is obviousthat this method which results in an increased number of elements hasthe same disadvantages as does the method of thickening the poles.

It is, therefore, the primary object of the present invention to improvethe broadband properties of dualpolarized antennas while maintaining theconstruction costs low.

More specifically, this object is attained by placing the polarizationplanes of the standard narrow band dual polarized antennas at an angleof 45 degrees against the principal axes of the antenna elements bymeans of hybrid or bridge coupling circuits in the feed system.

The exact nature of this invention as well as other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification relating to the annexed drawing, in which:

FIG. 1 is a diagrammatic view of one embodiment of the invention;

FIG. 2 is a diagrammatic view of another form of the invention;

FIG. 3 is a diagrammatic view of the device of FIG. 2 mounted in anarray;

FIG. 4 is a perspective view, partly diagrammatic, of still another formof the invention; and

FIG. 5 is a section of the device shown in FIG. 4.

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts through Patented Dec. 12, 1967'out the several views, there is shown in FIG. 1 a dualpolarizedturnstile antenna 10 comprising two sets of orthogonally spaced dipolescrossed at their centers. Antenna elements 12 and 13 make up one of thesets of dipoles and elements 14 and 15 make up the other set. Elements12, 13, 14, and 15 lie in the same plane and are, therefore, arranged infourfold axial symmetry. A first transformer 17 has its secondarycoupled between the feed points of elements 12 and 15. A secondtransformer 18 is shielded from the first transformer 17 and has itssecondary coupled between the feed points of elements 13 and 14. Theprimaries of transformers 17 and 18 are connected in parallel with eachother and across a first pair of input terminals 20 and 21. A secondpair of input terminals 22 and 23 are connected to the midpoints of thesecondary windings of transformers 17 and 18 respectively. The sense ofthe windings on transformers 17 and 18 are such that poles 13 and 15will be fed in phase and fed against poles 14 and 12 as seen by inputterminals 20 and 21. The resulting plane of polarization for inputterminals 20 and 21 will, therefore, be inclined at 45 degrees withrespect to the antenna poles and extend from the upper right side to thelower left side as viewed in FIG. 1. As seen from input terminals 22 and23, elements 13 and 14 will be fed in phase and fed against elements 12and 15 which are also fed in phase. This is true, because the inputs 22and 23 are connected to the midpoints of transformers 17 and 18, therebycausing the effect of one half of the transformer to cancel out theelfect of its other half. The plane of polarization for inputs 22 and 23will, therefore, be perpendicular to the plane of polarization forinputs 20 and 21.

From the impedance viewpoint, each input is effectively feeding a dipolewherein each dipole half consists of two conductors or antenna elements.For example, with respect to inputs 20 and 21, the combination ofelements 13 and 15 are equivalent to a dipole half while the combinationof elements 12 and 14 are equivalent to the other half. Such anarrangement will result in a bandwidth which is wider thanthe bandwidthof standard turnstile antennas wherein each input feeds only twoconductors or antenna elements as is well known from conventionalbroad-banding techniques. In other words, because each input feeds onepair of antenna elements against another pair of elements the equivalentQ of the antenna is lower than an antenna having only one element fedagainst another, assuming, of course, equal thickness for the elements.Because the Q is lower, the bandwidth will obviously be broader.

The device of FIG. 2 utilizes the same principles described above forthe device of FIG. 1. However, a slightly different feed system is used.The feed points of elements 12, 13, 14, and 15 are connected by chokes25, 26, 27, and 28. These chokes are shielded from each other. However,each choke is tightly coupled to itself as indicated by the parallellines which represents a ferrite core or the like. The input terminals20, 21, 22, and 23 are each connected to the midpoints of chokes 25, 26,27, and 28 respectively. It is, therefore, evident that with respect toinput 20, for example, one half of choke 25 will cancel out the effectof the other half of choke 25 and input 20 will be coupled to elements13 and 15 through a low impedance. However, chokes 27 and 28 willpresent a high impedance to input terminal 20. In a like manner a lowimpedance will couple terminal 21 to elements 12 and 14, terminal 23 toelements 13 and 14, and terminal 22 to elements 12 and 15. We,therefore, have a dual-polarized antenna with two orthogonal lanes ofpolarization inclined at an angle of 45 degrees with respect to theelements 12 and 15. This results in the same situation as was describedfor the device of FIG. 1. Of course, as in standard turnstile antennas,the resultpair of axially spaced, dual-polarized antennas fed in phaseopposition. Such arrays, beyond being directional,

are also useful for creating a neutral axis wherein the antenna mast andfeed lines are mounted without affecting the radiation. Since theantennas are fed in phase opposition the neutral axis will be midwaybetween the antennas. The manner of feeding such an array to obtainphase opposition is shown in FIG. 3, i.e., corresponding elements on theantennas are connected to the same input terminals but in a reversedmanner. For example, the pair of elements 12 and 15 are connected toterminal 22" while elements 12" and 15" are connected to terminal 23.

FIGS. 1-3 show the antenna elements in the form of linear dipoles. Ofcourse, these elements are only representative and may be replaced by,end-loaded dipoles, folded dipoles, loop antennas, biconical antennas,etc. The principles of the invention may be carried out as long as thereare four identical antenna elements arranged in fourfold axial symmetry.

FIGS. 4 and show the principles of the invention applied to a squarehorn antenna having four antenna elements or tapered ridges 30, 31, 32,and 33 arranged in fourfold axial symmetry inside a square waveguidesection 34. One end of the section 34 is terminated in a quarter-wavecavity 35 and the other end is connected to the throat of afiared horn36. Ridges 30-33 at the wide end adjacent cavity 35 are connected toeach other by chokes 25, 26, 27, and 28. A pair of input lines in theform of coaxial lines 37 and 38 pass through the 1 rear wall of cavityand have their outer conductors connected to the midpoints of chokes 27and 2S respectively. The center conductors of lines 37 and 38 areconnected to the midpoints of chokes 28 and 26 and to the shortedquarter-wave stubs 39 and 40 respectively. Quarter-wave stubs 39 and 40are in effect dummy coaxial conductors and provide a balancedtransformation from lines 37 and 38 respectively to the ridges 30, 31,32, and 33(With respect to input lines 37, ridges 31 and 32 will be fedin phase and against ridges 30 and 33. With respect to input line 38ridges 32 and 33 will be fed in phase and against ridges 30 and 31. 7

It should 'be understood of course, that the foregoing disclosurerelates to only preferred embodiments of the invention and that numerousmodifications or alterations may be made therein Without departing fromthe spirit pended claims.

What is claimed is:

1. A daul-polarized antenna comprising; four identical antenna elementsarranged in fourfold axial symmetry; first and second inputs; first andsecond transformers, said first input connected across the primaries ofsaid transformers; the secondary of said first transformer connectedbetween one adjacent pair of said antenna elements; the secondary ofsaid second transformer connected between the other pair of said antennaelements opposed thereto; and the terminals of said second inputconnected to the midpoints of said secondaries of said first and secondtransformers respectively.

2. The antenna according to claim 1, and wherein said four antennaelements form two linear dipole antennas mounted normal to each otherand intersecting at their midpoints.

3. The antenna according to claim 1, and wherein said four antennaelements are coupled to a horn antenna.

4. The antenna according to claim 3, and wherein said horn is squareshaped and said elements are tapered ridges mounted in a squarewaveguide which terminates in a cavity at one end and is connected tosaid horn'at the other end thereof.

5. A dual-polarized antenna comprising four antenna elements arranged infourfold axial symmetry; first and second inputs; four choke coils; eachsaid coil connected between a different pair of adjacent antennaelements; said first input connected to the midpoints of onepair ofopposed coils; and said second input connected to the midpoints of theother pair of opposed coils.

6. The antenna according to claim 5 and wherein said four antennaelements form two linear dipole antennas mounted normal to each otherand intersecting at their midpoints.

7. The antenna according to claim 5 and wherein said four antennaelements are coupled to a horn antenna. 8. The antenna according toclaim 7, and wherein said horn is square shaped and said elements aretapered ridges mounted in a square waveguide which terminates in acavity at one end and is connected to said horn at the other endthereof.

References Cited UNITED STATES PATENTS 2,374,271 4/1945 Brown 3437982,581,352 1/1952 Bliss 343-797 3,248,736 4/ 1966 Bohar 343-797 ELI.LIEBERMAN, Primary Examiner.

1. A DAUL-POLARIZED ANTENNA COMPRISING; FOUR IDENTICAL ANTENNA ELEMENTSARRANGED IN FOURFOLD AXIAL SYMMETRY; FIRST AND SECOND INPUTS; FIRST ANDSECOND TRANSFORMERS, SAID FIRST INPUT CONNECTED ACROSS THE PRIMARIES OFSAID TRANSFORMERS; THE SECONDARY OF SAID FIRST TRANSFORMER CONNECTEDBETWEEN ONE ADJACENT PAIR OF SAID ANTENNA ELEMENTS; THE SECONDARY OFSAID SECOND TRANSFORMER CONNECTED BETWEEN THE OTHER PAIR OF SAID ANTENNAELEMENTS OPPOSED THERETO; AND THE TERMINALS OF SAID SECOND INPUTCONNECTED TO THE MIDPOINTS OF SAID SECONDARIES OF SAID FIRST AND SECONDTRANSFORMERS RESPECTIVELY.